Isolable Cu(I) Complexes of Extremely Electron-Poor, Completely Unreduced o -Quinone and “Di- o -Quinone” Ligands Stabilized through π–π Interactions in the Secondary Coordination Sphere

Abstract

The copper?quinone interaction plays important roles in diverse fields such as biochemistry, catalysis, and optically/magnetically switchable materials. Despite this fact, the isolation and thorough characterization of copper(I)-quinone complexes remains a highly challenging task owing to their intrinsic instability. We herein present systems where the stability imparted by the extended π-system of a pyrene ring is used to synthesize, isolate, and crystallographically characterize the first example of a dinuclear metal complex that is bridged by a completely unreduced ?di-o-quinone?-type ligand. Additionally, we present the monocopper counterpart with the o-quinone?pyrene type of ligand. The copper complexes are redox-rich and display intriguing electrochemical, optical, and electron paramagnetic resonance (EPR) spectroscopic properties. The line-rich EPR spectra of the one-electron reduced copper(I) complexes were simulated and analyzed via density functional theory calculations. The results presented here establish π?π stacking as a viable alternative to stabilize otherwise unstable redox-active compounds with possible consequences for sensing and redox catalysis.